U.S. patent number 7,298,598 [Application Number 11/237,399] was granted by the patent office on 2007-11-20 for wiring device with multi-shot miswire.
This patent grant is currently assigned to Pass & Seymour, Inc. Invention is credited to Kent Morgan, Thomas N. Packard, Jeffrey C. Richards.
United States Patent |
7,298,598 |
Morgan , et al. |
November 20, 2007 |
Wiring device with multi-shot miswire
Abstract
The present invention is directed to a protective wiring device
that includes a plurality of line terminals coupled to a plurality
of load terminals by way of at least one conductive path. A miswire
detection circuit is coupled to the at least one conductive path.
The miswire detection circuit is configured to monitor signal
propagation characteristics on the at least one conductive path and
generate a miswire detection signal based on the signal propagation
characteristics commencing each time source power is applied to
either the plurality of line terminals or the plurality of load
terminals. A fault detection circuit is coupled to the at least one
conductive path. The fault detection circuit is configured to
detect a fault condition propagating on the at least one conductive
path. The fault detection circuit is configured to generate a trip
signal in response to either the fault condition or the miswire
detection signal. A circuit interrupter is coupled to the fault
detection circuit. The circuit interrupter is configured to
introduce an electrical discontinuity in the at least one
conductive path in response to the trip signal.
Inventors: |
Morgan; Kent (Groton, NY),
Richards; Jeffrey C. (Baldwinsville, NY), Packard; Thomas
N. (Syracuse, NY) |
Assignee: |
Pass & Seymour, Inc
(Syracuse, NY)
|
Family
ID: |
38690969 |
Appl.
No.: |
11/237,399 |
Filed: |
September 28, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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10884304 |
Jul 2, 2004 |
7133266 |
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11103722 |
Apr 12, 2005 |
7212386 |
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10900769 |
Jul 28, 2004 |
7154718 |
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Current U.S.
Class: |
361/45;
324/424 |
Current CPC
Class: |
H02H
3/338 (20130101) |
Current International
Class: |
H02H
3/02 (20060101); G01R 31/02 (20060101) |
Field of
Search: |
;361/42,45,77 ;307/127
;324/424,521 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Sherry; Michael
Assistant Examiner: Benenson; Boris
Attorney, Agent or Firm: Malley; Daniel P. Bond, Schoeneck
& King PLLC
Parent Case Text
CROSS-REFERENCE TO RELATED APPLICATIONS
This is a continuation-in-part of U.S. patent application Ser. No.
10/884,304 filed on Jul. 2, 2004 now U.S. Pat. No. 7,133,266, U.S.
patent application Ser. No. 11/103,722 filed on Apr. 12, 2005 now
U.S. Pat. No. 7,212,386, and U.S. patent application Ser. No.
10/900,769 filed on Jul. 28, 2004 now U.S. Pat. No. 7,154,718, the
contents of which are relied upon and incorporated herein by
reference in their entirety, and the benefit of priority under 35
U.S.C. .sctn. 120 is hereby claimed.
Claims
What is claimed is:
1. A protective wiring device comprising: a plurality of line
terminals coupled to a plurality of load terminals by way of at
least one conductive path; a miswire detection circuit coupled to
the at least one conductive path, the miswire detection circuit
being configured to monitor signal propagation characteristics on
the at least one conductive path and generate a miswire detection
signal based on the signal propagation characteristics commencing
each time source power is applied to either the plurality of line
terminals or the plurality of load terminals; a fault detection
circuit coupled to the at least one conductive path, the fault
detection circuit being configured to detect a fault condition
propagating on the at least one conductive path, the fault
detection circuit being configured to generate a trip signal in
response to either the fault condition or the miswire detection
signal; and a circuit interrupter coupled to the fault detection
circuit, the circuit interrupter being configured to introduce an
electrical discontinuity in the at least one conductive path in
response to the trip signal.
2. The device of claim 1, wherein the signal propagation
characteristics include a line voltage polarity and a load current
polarity.
3. The device of claim 2, wherein the miswire detection circuit
includes a comparator circuit configured to compare the line
voltage polarity and the load current polarity, the miswire
detection circuit generating the miswire detection signal based on
the comparison of line voltage polarity and the load current
polarity.
4. The device of claim 1, wherein the miswire detection circuit
further comprises: a current sensor coupled to the at least one
conductive path, the current sensor being configured to monitor a
load current polarity; a voltage sensor coupled to the at least one
conductive path, the voltage sensor being configured to monitor a
line voltage polarity; and a processor coupled to the current
sensor and the voltage sensor, the processor being configured to
generate the miswire detection signal based on a comparison of the
line voltage polarity and the load current polarity.
5. The device of claim 4, wherein the current sensor includes a
shunt and/or current transformer.
6. The device of claim 4, wherein an electric load is coupled to
the plurality of line terminals, and wherein the processor is
configured to generate the miswire detection signal when the line
voltage polarity and the load current polarity are opposite to each
other during a predetermined time interval.
7. The device of claim 4, further comprising an internal electric
load disposed between the current sensor and the circuit
interrupter, whereby the processor is configured to generate the
miswire detection signal when the current flowing through the
internal electric load not being sensed by the current sensor.
8. The device of claim 7, wherein the processor is configured to
generate the miswire detection signal when a load current polarity
flowing through an external load connected to the line terminals
and the line voltage polarity are opposite to each other.
9. The device of claim 4, further comprising an internal electric
load disposed between the current sensor and the plurality of line
terminals, whereby a miswire detection signal is not generated when
the current flowing through the internal electric load is not
sensed by the current sensor.
10. The device of claim 9, wherein the processor is configured to
generate the miswire detection signal when a polarity of a current
flowing through the internal load and the line voltage polarity
oppose each other.
11. The device of claim 1, wherein the fault detection circuit
further comprises: a sensor coupled to the at least one conductive
path, the sensor being configured to sense differential current
propagating on the at least one conductive path; a detector circuit
coupled to the sensor, the detector being configured to detect a
fault condition propagating on the at least one conductive path if
the differential current exceeds a predetermined amount and
generate the trip signal in response thereto; a switch element
coupled to the detector and the processor, the switch element being
configured to provide a switching current in response to the trip
signal and the miswire detection signal; and a solenoid element
coupled to the switch element, the solenoid being configured to
actuate the circuit interrupter in response to the switching
current.
12. The device of claim 6, further comprising an internal electric
load, wherein the miswire detection circuit further comprises a
processor circuit configured to direct a pulsed current into the
internal electric load, the processor being configured to generate
the miswire detection signal based on a polarity of the pulsed
current flowing through the internal electric load compared to the
line voltage polarity.
13. The device of claim 12, further comprising a transistor coupled
between the internal electric load and the processor, the pulsed
current being propagated by the transistor in response to the
processor pulsing the transistor into an ON state at a
predetermined repetition rate.
14. The device of claim 12, wherein the internal electric load
includes a solenoid element.
15. The device of claim 12, wherein the internal electric load
includes a resistance.
16. The device of claim 1, wherein the signal propagation
characteristics include an electrical current.
17. The device of claim 16, wherein the miswire detection circuit
includes a reclosable fuse.
18. The device of claim 17, wherein the reclosable fuse is
configured to remain closed whenever the source voltage is
connected to the plurality of load terminals, and wherein the
reclosable fuse is configured to open whenever the source voltage
is connected to the plurality of line terminals for a predetermined
period of time.
19. The device of claim 17, wherein the reclosable fuse is
configured to close each time that the device is removed from
and/or installed in the electrical distribution system.
20. The device of claim 17, further comprising: a housing
configured to accommodate the plurality of line terminals, the
plurality of load terminals, and the circuit interrupter; a printed
circuit board including the miswire detection circuit and the fault
detection circuit at least partially disposed thereon, the
reclosable fuse being mounted on the printed circuit board; and an
actuator probe coupled to the reclosable fuse and partially
accessible from an exterior portion of the housing, the actuator
probe being configured to close the reclosable fuse.
21. The device of claim 20, wherein the actuator probe is prevented
from closing the reclosable fuse when a wall plate is attached to
the housing.
22. The device of claim 20, wherein the actuator probe maintains
the reclosable fuse in a closed state if a wall plate is not
attached to the housing, and wherein the circuit interrupter is
prevented from resetting after the discontinuity is introduced.
23. The device of claim 17, wherein the reclosable fuse closes in
response to a removal of a wall plate from the device.
24. The device of claim 17, wherein the miswire detection circuit
includes a heating element that generates heat to open the
reclosable fuse within a predetermined period of time.
25. The device of claim 1, wherein the miswire detection circuit
includes a voltage sensor that generates a voltage signal in
response to the source voltage; a current sensor that generates a
current signal in response to the load current; and a processor
that compares the voltage signal to the current signal to generate
the trip signal based on a predetermined relationship between the
voltage signal and the current signal.
26. The device of claim 25, wherein the predetermined relationship
includes polarity comparison between the voltage signal and the
current signal.
27. The device of claim 25, wherein the predetermined relationship
includes a phase comparison between the voltage signal and the
current signal.
28. The device of claim 25, wherein the device further includes a
first internal load such that the current sensor generates a
current signal in response to the first internal load current but
only when the source voltage is connected to the plurality of line
terminals.
29. The device of claim 28, wherein the processor is configured to
enable current flow through the first internal load for a
predetermined period of time.
30. The device of claim 29, wherein the predetermined period of
time occurs a predetermined interval of time after a voltage zero
crossing.
31. The device of claim 28, wherein the first internal load
includes a trip solenoid that causes the circuit interrupting
assembly to enter the tripped state in response to the trip
signal.
32. The device of claim 28, wherein the device further includes a
second internal load, such that the current sensor generates a
current signal in response to second internal load current but only
when the source voltage is connected to the plurality of load
terminals.
33. The device of claim 1, wherein the circuit interrupter includes
isolating contacts that disconnect one or more sets of the
plurality of line terminals from the plurality of load terminals
when the circuit interrupter is in the tripped state.
34. The device of claim 1, wherein the miswire detection circuit
includes isolating contacts that disconnect one or more sets of the
plurality of line terminals from the plurality of load terminals
when the miswire detection circuit detects that source voltage has
been connected to the plurality of load terminals.
35. The device of claim 1, wherein the miswire detection circuit
includes an indicator that visibly and/or audibly indicates when
the miswire detection circuit detects that source voltage has been
connected to the plurality of load terminals.
36. The device of claim 1, wherein the detected condition includes
a ground fault condition, an arc fault condition, a grounded
neutral condition, a miswire fault condition, and/or a simulated
test fault condition.
37. A method for wiring a protective device in an electrical
circuit, the protective device including a plurality of line
terminals coupled to a plurality of load terminals by way of at
least one conductive path, the method comprising: (a) connecting
the plurality of load terminals to source voltage; (b) monitoring
signal propagation characteristics on the at least one conductive
path, the step of monitoring commencing each time source voltage is
applied to the plurality of load terminals; (c) generating a
miswire trip signal based on a predetermined signal propagation
characteristic; and (d) introducing an electrical discontinuity in
the at least one conductive path in response to the trip
signal.
38. The method of claim 37, further comprising: (e) resetting the
protective device, whereby electrical continuity in the at least
one conductive path is restored; (f) monitoring the signal
propagation characteristics; (g) generating the miswire trip signal
based on a predetermined signal propagation characteristic; (h)
introducing an electrical discontinuity in the at least one
conductive path in response to the miswire trip signal; and (i)
repeating steps (e)-(i) until the plurality of load terminals are
disconnected from the source voltage.
39. The method of claim 37, further comprising: (j) connecting the
plurality of line terminals to the source voltage; (j) disabling
steps (a) through (d) after a predetermined time interval elapses.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to electrical wiring
devices, and particularly to protective wiring devices.
2. Technical Background
AC power is provided to a house, building or other such facilities
by coupling one or more breaker panels to an electrical
distribution system, or another such source of AC power. The
breaker panel distributes AC power to one or more branch electric
circuits installed in the structure. The electric circuits
typically include one or more receptacle outlets and may further
transmit AC power to one or more electrically powered devices,
commonly referred to in the art as load circuits. The receptacle
outlets provide power to user-accessible loads that include a power
cord and plug, with the plug being insertable into the receptacle
outlet. Because certain types of faults have been known to occur in
electrical wiring systems, each electric circuit typically employs
one or more electric circuit protection devices. Electric circuit
protective devices have been disposed within the breaker panel,
receptacle outlets, plugs and the like.
Both receptacle wiring devices and electric circuit protective
wiring devices in general, are disposed in an electrically
non-conductive housing. The housing includes electrical terminals
that are electrically insulated from each other. The line terminals
are intended to be connected by the installer to a power source of
an electrical distribution system, and the feed-through load
terminals are intended to be connected to provide the electrical
power to downstream receptacles, lighting fixtures, switches, and
the like. Receptacle load terminals are electrically connected to
the feed-through load terminals. The receptacle load terminals are
configured to align with the blades of an attachment plug in order
to provide source power by way of the plug to a user attachable
load. Protective devices typically include a circuit interrupter
that connects the line terminals to the load terminals in the reset
state and disconnects the line terminals from the feed-through and
receptacle load terminals in the tripped state. The circuit
interrupter trips when a fault condition occurs. There are various
types of protective devices including ground fault circuit
interrupters (GFCIs), ground-fault equipment protectors (GFEPs),
and arc fault circuit interrupters (AFCIs). Some protective devices
include both GFCIs and AFCIs.
An arc fault typically manifests itself as a high frequency current
signal. Accordingly, an AFCI may be configured to detect various
high frequency signals and de-energize the electrical circuit in
response thereto. A ground fault occurs when a current carrying
(hot) conductor creates an unintended current path to ground. A
differential current is created between the hot/neutral conductors
because some of the current flowing in the circuit is diverted into
the unintended current path. The unintended current path represents
an electrical shock hazard. Ground faults, as well as arc faults,
may also result in fire.
A "grounded neutral" is another type of ground fault. This type of
fault may occur when the load neutral terminal, or a conductor
connected to the load neutral terminal, becomes grounded. While
this condition does not represent an immediate shock hazard, it may
lead to serious hazard. As noted above, a GFCI will trip under
normal conditions when the differential current is greater than or
equal to approximately 6 mA. However, when the load neutral
conductor is grounded the GFCI becomes de-sensitized because some
of the return path current is diverted to ground. When this
happens, it may take up to 30 mA of differential current before the
GFCI trips. Therefore, if a double-fault condition occurs, i.e., if
the user comes into contact with a hot conductor (the first fault)
when simultaneously contacting a neutral conductor that has been
grounded on the load side (the second fault), the user may
experience serious injury or death.
Another type of fault condition is commonly referred to as
miswiring, or reverse wiring. A protective device may be miswired
during installation by connecting the load terminals to AC power.
When this happens, the circuit interrupter may be unable to
interrupt the flow of electrical current to the receptacle
terminals when a fault condition is present. Unfortunately,
protective devices do not typically alert the user to the miswire
condition. Thus, it is not until damage or injury occur that the
miswired condition is evident. As noted above, receptacle load
terminals and the feed-through load terminals may be permanently
connected by an electrical conductor. When a device is properly
wired, the circuit interrupter typically includes a single breaker
that breaks the connection between the line terminals and both the
feed-through load terminals and the receptacle load terminals. In
other words, the typical protective device is not configured to
remove power from the user load when a hazardous fault condition is
extant. Accordingly, when a receptacle type device is reverse
wired, unprotected AC power may be available at the receptacle load
terminals when the circuit interrupter is in the tripped state.
Protective devices may be equipped with a test button. However,
while test buttons may be determine the ability of the protective
device to detect and interrupt a fault condition, they are
typically not configured to reveal a reverse-wired condition.
Accordingly, many devices are provided with wiring instruction
sheets. Unfortunately, instruction sheets are often ignored by
installers.
In one approach that has been considered, a protective device is
equipped with a barrier(s) that is/are configured to prevent
circuit reset until AC voltage is present at the line terminals.
The barrier may alert the installer to the reverse-wired condition
by preventing reset of the device and by denying AC power to the
feed-through load. This approach may be effective during the
original installation of the protective device. However, once
proper installation is effected the barrier is deactivated and
inoperative during a subsequent re-installation. This drawback is
further exacerbated by the fact that the installation instructions
are unlikely to be available for any re-installation.
In another approach that has been considered, a protective device
may be equipped with a fuse that is configured to prevent circuit
interrupter reset until AC voltage is provided to the line
terminals. The fuse circuit prevents reset of the device and denies
power to the feed-through load until proper wiring is effected.
Once proper wiring is effected, the fuse blows and is no longer
available to detect a reverse-wired condition if there is a
reinstallation. Again, making matters worse, the installation
instructions are likely to be lost and not available for any
re-installation.
In another approach that has been considered, a protective device
may be equipped with one or more sets of isolating contacts
disposed between the feed-through load terminals and the receptacle
load terminals. In this approach, the set of isolating contacts may
be controlled by a miswire detection circuit. In the event of a
miswire condition, the miswire detection circuit is configured to
either open (or prevent closure) of the isolating contacts. After a
proper wiring condition is detected, the miswire detection circuit
is configured to either close (or permit closure) of the isolating
contacts. Like the other approaches considered above, the miswire
detection circuit is ineffectual after an initial proper
installation, and is no longer available to detect a reverse-wired
condition during any reinstallation. Thus, the isolating contacts
are closed in spite of a reverse wired condition.
What is needed is a protective device that denies power to the
protected circuit, including receptacle terminals, during a
miswired condition. Further, a protective device, responsive to the
miswired condition during each and every installation, is
needed.
SUMMARY OF THE INVENTION
The present invention addresses the needs described above. In
particular, the present invention is directed to a protective
device that denies power to the protected circuit, including
receptacle terminals, during a miswired condition. More
importantly, the protective device of the present invention is
responsive to the miswired condition during each and every
installation.
One aspect of the present invention is a protective wiring device
that includes a plurality of line terminals coupled to a plurality
of load terminals by way of at least one conductive path. A miswire
detection circuit is coupled to the at least one conductive path.
The miswire detection circuit is configured to monitor signal
propagation characteristics on the at least one conductive path and
generate a miswire detection signal based on the signal propagation
characteristics commencing each time source power is applied to
either the plurality of line terminals or the plurality of load
terminals. A fault detection circuit is coupled to the at least one
conductive path. The fault detection circuit is configured to
detect a fault condition propagating on the at least one conductive
path. The fault detection circuit is configured to generate a trip
signal in response to either the fault condition or the miswire
detection signal. A circuit interrupter is coupled to the fault
detection circuit. The circuit interrupter is configured to
introduce an electrical discontinuity in the at least one
conductive path in response to the trip signal.
In another aspect, the present invention is directed to a method
for wiring a protective device in an electrical circuit. The
protective device includes a plurality of line terminals coupled to
a plurality of load terminals by way of at least one conductive
path. The method includes connecting the plurality of load
terminals to source voltage. Signal propagation characteristics on
the at least one conductive path are monitored, monitoring
commencing each time source voltage is applied to the plurality of
load terminals. A miswire trip signal is generated based on a
predetermined signal propagation characteristic. An electrical
discontinuity is introduced in the at least one conductive path in
response to the trip signal.
Additional features and advantages of the invention will be set
forth in the detailed description which follows, and in part will
be readily apparent to those skilled in the art from that
description or recognized by practicing the invention as described
herein, including the detailed description which follows, the
claims, as well as the appended drawings.
It is to be understood that both the foregoing general description
and the following detailed description are merely exemplary of the
invention, and are intended to provide an overview or framework for
understanding the nature and character of the invention as it is
claimed. The accompanying drawings are included to provide a
further understanding of the invention, and are incorporated in and
constitute a part of this specification. The drawings illustrate
various embodiments of the invention, and together with the
description serve to explain the principles and operation of the
invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of a protective device in accordance
with a first embodiment of the present invention;
FIG. 2 is a schematic of the protective device shown in FIG. 1 in a
miswired state;
FIG. 3 is a schematic diagram in accordance with a second
embodiment of the present invention;
FIG. 4 is a schematic diagram in accordance with a third embodiment
of the present invention;
FIGS. 5A-5E are timing diagrams illustrating the miswire protection
functionality of the present invention;
FIG. 6 is a schematic of a miswire lockout circuit in accordance
with a fourth embodiment of the present invention;
FIG. 7 is a front cover view of a protective device in accordance
with the present invention;
FIGS. 8-9 are cross-sectional views of the protective device in
accordance with an embodiment of the present invention; and
FIGS. 10-11 are cross-sectional views of the protective device in
accordance with an alternate embodiment of the present
invention.
DETAILED DESCRIPTION
Reference will now be made in detail to the present exemplary
embodiments of the invention, examples of which are illustrated in
the accompanying drawings. Wherever possible, the same reference
numbers will be used throughout the drawings to refer to the same
or like parts. An exemplary embodiment of the protective device of
the present invention is shown in FIG. 1, and is designated
generally throughout by reference numeral 10.
As described in more detail below, protective device 10 includes a
plurality of line terminals coupled to a plurality of load
terminals by way of at least one conductive path. When the
plurality of load terminals are connected to source voltage, device
10 monitors signal propagation characteristics on the at least one
conductive path. Device 10 is configured such that the step of
monitoring commences each time source voltage is applied to the
plurality of load terminals. A miswire trip signal is generated
based on a predetermined signal propagation characteristic. An
electrical discontinuity is introduced in the at least one
conductive path in response to the trip signal.
Referring to FIG. 1 and FIG. 2, a schematic diagram of a protective
device 10 in accordance with a first embodiment of the present
invention is disclosed. FIG. 2 is a schematic diagram of the
protective device in a miswired state.
Device 10 typically includes a hot line terminal 12 and a neutral
line terminal 14. Line terminals 12, 14 are coupled to sensor 26
and sensor 28 by way of a hot conductive path and a neutral
conductive path, respectively. The conductive paths are connected
to circuit interrupter 24. Circuit interrupter 24 couples the line
terminals (12, 14) to the feed-through terminals (16, 18) and the
receptacle terminals (20, 22) when circuit interrupter 24 is in a
reset state. Those of ordinary skill in the art will understand
that load terminals 16, 18, may be connected to wires coupled to
one or more downstream receptacles, or switches, in a daisy chain
arrangement. Receptacle terminals 20, 22 are configured to mate
with an appliance plug connected by a power cord to an electrical
appliance or a similar electrical load. Of course, circuit
interrupter 24 disconnects the line terminals from both the load
terminals 16, 18 and the receptacle load terminals 20, 22 in the
tripped state.
In one embodiment of the present invention, isolating contacts 30
are configured to disconnect one or more of the feed-through
terminals 16, 18 from a corresponding receptacle terminal 20, 22.
Such contacts are open when the device has been miswired. Isolating
contacts 30 are coupled operably to circuit interrupter 24 such
that they are open when circuit interrupter 24 is in the tripped
state. Alternatively, isolating contacts 30 are coupled operably to
a supplementary interrupter (not shown) such that they are open
when device 10 has been miswired.
Device 10 operates as follows. Sensor 26 is a differential
transformer which is configured to sense load-side ground faults.
Sensor 28 is a grounded neutral transformer and is configured to
generate and couple a fault signal to the differential transformer
in the event of a grounded-neutral fault condition. Differential
transformer 26 and grounded-neutral transformer 28 are coupled to
detector circuit 32. Power supply circuit 34 conditions AC power by
providing a DC (V+) voltage supply for GFCI detector circuit 32.
Detector 32 provides a fault detect output signal 36 in response to
sensor inputs from transformers (26, 28.) Output signal 36 is
directed into filter circuit 38. The filtered output signal is
provided to the control input of SCR 40. SCR 40 is turned ON to
energize solenoid 42 when it is turned ON by the filtered output
signal. Solenoid 42 drives trip mechanism 44 to open the
interrupting contacts in circuit interrupter 24.
The trip solenoid 42 remains energized until the contacts in
circuit interrupter 24 are tripped. The open contacts interrupt the
flow of fault current. The sensor output signal generated by
transformer 26 is also terminated by the interruption of the fault
current. When the transformer signal ceases, the detector output
signal changes state turning SCR 40 OFF. Once SCR 40 is OFF,
solenoid 42 de-energizes within a time period that is less than
about 25 milliseconds. After the fault condition has been
eliminated, reset button 46 may be employed to reset circuit
interrupter 24.
Device 10 also is equipped with a test facility. In particular,
when test button 48 is depressed by a user, a simulated fault
condition is generated. The simulated fault condition is used to
check the operative condition of GFCI 10. Circuit interrupter 24
will trip if the device is properly operating. Power may be
restored to device 10 after a successful test by pressing reset
button 46. In an alternative embodiment of the present invention,
the test facility can be actuated by depressing the reset button
46. Switch contacts in communication with reset button 46 close the
test circuit to initiate the test in the manner previously
described.
Device 10 includes a miswire lock-out circuit 50. Miswire lock-out
circuit 50 includes a voltage sensor 52 that monitors the polarity
of the AC (or DC) source voltage. Current transformer 54 monitors
the direction of the current (i.e., current polarity) from the
voltage source to load 60. When device 10 is properly wired as
shown in FIG. 1, the current transformer also monitors the current
through a user attachable load 62. If the polarity of the current
and the polarity of the voltage match each other, processor 56
determines that device 10 has been properly wired.
Referring to FIG. 2, if the current and voltage polarities oppose
each other, processor 56 determines that device 10 has been reverse
wired. In response to a reverse wired condition, processor 56 sends
a signal to SCR 40 to turn ON, causing circuit interrupter 24 to
trip. If the reset button 46 is operated, circuit interrupter 24
momentarily resets, but trips soon thereafter when the miswired
condition is again detected by processor 56. The circuit
interrupter will continue to trip until the reverse wiring
condition is corrected. It is noted that device tripping is
automatic, i.e., the installer does not have to manually operate
the test facility or manually perform some other action to initiate
lock-out. However, sensing current has been described as a
prerequisite for determining proper or reverse wiring. Therefore
the device will fail to lock-out, even if a miswired condition is
present, until such time as a load (60, 62) is connected to the
device to generate the current. It is desirable for device 10 to
lock-out in response to a miswired condition without having to wait
until an external load is connected.
In an alternate embodiment, device 10 may include an internal load
64 disposed between current transformer 54 and circuit interrupter
24. Internal load 64 operates in a similar manner to external load
60 by generating a current flow having a polarity indicative of
proper wiring. Unlike load 60, load 64 does not generate a current
flow through transformer 54 when device 10 is reverse wired. Thus,
when device 10 includes an internal load, lock-out circuit 50 is
configured to permit device 10 to reset when the current polarity
and the voltage polarity match each other. On the other hand,
lock-out circuit 50 is configured to trip device 10 when the
current polarity and the voltage polarity oppose each other or when
no load current is being sensed by transformer 54 (i.e., before
device is connected to an external miswired load 60).
Alternatively, an internal load 66 may be disposed between current
transformer 54 and the line terminals 12,14. Load 66 operates in a
similar manner to load 60 by generating a current flow through
transformer 54 indicative of reverse wiring. Unlike load 60, load
66 does not generate a current flow through transformer 54 when
device 10 is properly wired. In this embodiment, lock-out circuit
50 is configured to trip device 10 when the current polarity
through load 66 (with or without load 60) compared to the voltage
polarity oppose each other. On the other hand, lock-out circuit 50
is configured to permit device 10 to reset when the current
polarity and voltage polarity match each other, or when there is no
load current present. In yet another embodiment of the present
invention, loads 64 and 66 are both be included. This also avoids
the need for an external load in order to determine whether the
protective device has been properly wired.
Referring back to FIG. 1, a transistor 58 may be disposed between
SCR 40 and processor 56. Processor 56 pulses transistor 580N at a
predetermined repetition rate to initiate a current through
solenoid 42. However, while each pulse generates a current through
solenoid 42, the resulting energy in the solenoid is not enough to
actuate trip mechanism 44. Solenoid 42 functions as a pulsed load.
Processor 50 is configured to determine whether or not device 10 is
properly wired on the basis of the direction (polarity) of the
pulsed current through solenoid 42 with respect to the voltage
polarity. Processor may make a miswire determination on the basis
of one or more pulses.
In another embodiment, solenoid 42 may be connected between current
transformer 54 and circuit interrupter 24. Alternatively, solenoid
42 may be connected between feed-through load terminals 16, 18 or
receptacle load terminals 20,22. In either case, transistor 58
pulses solenoid 42 in the manner previously described. Solenoid 42
again functions as a pulsed load.
In yet another embodiment, transistor 58 is configured to pulse
resistors 64 or 66 into conduction (not shown.) In general, the
benefit of pulsing the current through an internal load (64, 66,
42) is that a thermal dissipation rating of a load may be reduced
by more than ten-fold. Accordingly, the load may be
miniaturized.
In the embodiment shown in FIG. 1, an indicator 62 is coupled to
processor 56. Indicator 62 includes visible and/or audible
indication of a miswired condition. Processor 56 may provide a
repetitive signal to indicator 62, in which case indicator 62
provides a blinking and/or beeping indication of a miswired
condition.
While FIG. 1 and FIG. 2 are directed to ground fault detection
circuitry, the present invention is equally applicable to other
types of protective devices. Those of ordinary skill in the art
will recognize that substantially all of the various types of
protective devices include similar components for sensing,
detecting and interrupting the circuit interrupting contacts in
response to a particular fault condition. For example, the sensor
in an arc fault circuit interrupter (AFCI) is similar to
transformer 26 but is typically configured to sense load current
instead of differential current and/or line voltage. An AFCI sensor
may include at least one of a toroidal transformer, shunt or
voltage divider. Further, the detector in the AFCI may be
implemented as an integrated circuit similar in form factor to the
detector 32. The AFCI detector may also be configured to detect an
arc fault condition on the basis of the frequency spectrum of the
load current. Those of ordinary skill in the art will recognize
that an arc fault may exhibit high frequency noise burst patterns.
Once an arc fault condition has been detected, a signal is sent to
SCR 40 to trip the device.
Referring to FIG. 3, a schematic diagram in accordance with a
second embodiment of the present invention is disclosed. Miswire
lock-out circuit 300 is similar to lock-out circuit 50 shown in
FIGS. 1 and 2. The embodiment shown in FIG. 3 includes a shunt
sensor 302 coupled to processor 304. The function of sensor 302 is
similar to transformer 54. Processor 304 is configured to determine
the polarity of the load current using shunt sensor 302.
As embodied herein and depicted in FIG. 4, a schematic diagram in
accordance with a third embodiment of the present invention is
disclosed. This embodiment does not include a separate load current
polarity sensor per se. Instead, the protective device itself is
configured to determine the polarity of the load current. In
particular, miswire lock-out circuit 400 includes a switching
device 402 coupled to processor 400 by way of transistor 406.
Switching device 402 is open or closed in response to a signal from
processor 404. In particular, switching device 402 is opened or
closed in response to a signal from processor 404 by way of
transistor 406. When switching device 402 is open, currents through
line hot conductor 12 and line neutral conductor 14 flow equally
and oppositely through differential transformer 26. Accordingly,
the differential signal generated by transformer 26 is not
indicative of a fault (or simulated fault) condition. However, when
switching device 402 is closed, a portion of the load current
flowing through one or the other conductor is diverted through the
switching device. Since the currents in the two conductors are no
longer equal, a fault signal is provided to detector 32. Detector
32 provides an output load current signal to processor 404 on
detector output line 37. Processor 404 uses the output load current
signal to determine the load current polarity.
It is also noted that transistor 406 may perform a function similar
to that performed by transistor 58 in the embodiment depicted in
FIG. 1. Transistor 58 provided a pulsed signal to solenoid 42. In
response, solenoid 42 was momentarily driven into conduction to
provide a pulsed load current. Thus, the embodiment in FIG. 4
provides several means for detecting miswire, or reverse wiring,
conditions.
Device 10 is shown in FIG. 4 as being reverse wired. When the AC
(or DC) source voltage is positive during the time that switching
device 402 is closed, the direction of the summed current through
differential transformer 26 results in detector 32 providing a
negative current polarity signal to processor 404. Since the
voltage and current polarities oppose each other, processor 404
provides a signal to SCR 40 to trip circuit interrupter 24.
Switching device 402 may be closed by processor 400 only during the
negative half cycle intervals of the AC source voltage cycle. This
avoids the possibility of detector output signal 36 causing false
tripping since SCR 40 cannot turn ON during negative half
cycles.
FIGS. 5A-5E are timing diagrams illustrating the miswire protection
functionality of the present invention. The waveforms are described
using the references in FIG. 1 but are applicable to other
embodiments of the invention as well. The waveforms pertain to a
protective device 10 that is reverse-wired and in the reset state,
i.e., AC source voltage is connected to the device feed-through
terminals 16, 18.
FIG. 5A is a diagrammatic representation of the load current 502.
AC source voltage is applied to device 10 at time 500. Referring to
FIG. 5B, processor 56 generates a predetermined time delay interval
501 also commencing at time 500. The miswire lock-out circuit is
prevented from tripping even if there is a miswire condition, until
delay interval 501 elapses. Time interval 501 is pre-programmed
into processor 56 based on known transient noise properties.
Transient noise 505 may be generated by the initial application of
AC power to a device, or by the application of AC power after a
power outage. Accordingly, time interval 501 is programmed into
processor 56 to prevent transients 501 from initiating a false
lockout of device 10. Those of ordinary skill in the art will
understand that interval 501 is less than about 1 second.
FIG. 5C is a diagrammatic representation of the source voltage 503.
Note that AC source voltage 503 is out of phase with load current
502, shown in FIG. 5A. As noted previously, the out of phase
condition represents the fact that the protective device has been
reverse wired. Note also that AC source voltage 503 and load
current 502 are out of phase by a phase shift amount 506. Phase
shift 506 represents the possibility of an inductive load shift
that loads 64, 66, or 42, if provided, are unable to compensate
for.
As shown in FIG. 5D, processor 56 pulses a load into conduction
during an interval 508. As described above, the pulsing is
performed to compare the polarities of the load current and source
voltage. In the example provided by FIG. 5, the two signals are of
opposite polarity. Thus, processor 56 determines that device 10 has
been miswired. Processor 56 may be programmed such that interval(s)
508 occur only during the negative half cycles of the source
voltage for the reasons provided above.
Note also that interval(s) 508 must not be allowed to coincide with
intervals 506. Despite the fact that device 10 is miswired, the
load current and source voltage polarities match in these intervals
because of the phase shift 506. Processor 56 is programmed to delay
the commencement of interval 508 by a time period 510 from the
current zero crossing to avoid an erroneous wiring state indication
by processor 56.
Window interval 512 shown in FIG. 5E prevents the miswire detection
circuit from causing false tripping. Window 512 is initiated at
time 500 and elapses after a predetermined period of time has
transpired. Thus, the proper wiring/miswiring decision-making
process only occurs within window 512. Once the miswire lock-out
circuit 50 completes its task, it is prevented from causing false
tripping after interval 512 has elapsed.
As embodied herein and depicted in FIG. 6, a schematic of a miswire
lockout circuit in accordance with a fourth embodiment of the
present invention is disclosed. Reference is made to U.S. patent
application Ser. No. 10/884,304, which is incorporated herein by
reference as though fully set forth in its entirety, for a more
detailed explanation of a miswire circuit including a fuse. Miswire
lock-out circuit 600 is connected to the line side of circuit
interrupter 24. When protective device 10 is installed, fuse 602 is
closed. If the device is properly wired during the installation and
the source voltage is turned on, current through the circuit 600
generates a simulated fault current to trip the circuit interrupter
24. Current continues to flow through circuit 600 until a thermal
element 604 disposed in circuit 600 opens fuse 602, thus breaking
electrical connectivity in the circuit. Once electrical
connectivity is broken, the simulated fault current ceases,
permitting device 10 to be reset.
Assuming the device is reset, if the device is miswired during the
installation and the source voltage is turned on current flows
through circuit 600 by way of circuit interrupter 24. The simulated
fault current causes the circuit interrupter 24 to trip. In turn,
the fault current stops flowing by the tripping action. Note that
the circuit interrupter trips in response to the simulated fault
current typically in less than 25 milliseconds. The heat generated
in thermal element 604 during this time frame is insufficient to
open fuse 602. Accordingly, fuse 602 is operational until the
device is wired properly. Device 10 will continue to trip after
each reset until the device is wired properly.
In an alternate embodiment, fuse 602 is configured to self-heat in
response to the current flow, eliminating the need for thermal
element 604. Other miswire circuits are similar in performance to
circuit 600 but are re-configured to produce a signal or simulated
fault signal as appropriate for ground fault circuit interrupters,
arc fault circuit interrupters, combination arc fault and ground
fault circuit interrupters or other types of protective devices
(not shown.)
Fuse 602 may also be implemented using a resettable, or reclosable,
fuse. After device 10 is removed from an installation, fuse 602 is
closed to thereby restore miswire circuit 600. At this point, the
protective device is configured to enter a lock-out state in the
event of being miswired during re-installation.
FIGS. 7-11 illustrate a typical installation of the present
invention. Referring to FIG. 7, a front cover view of a protective
device in accordance with the present invention is disclosed.
Device 10 includes a front housing 750 that includes a flange 752.
The protective device is configured to be covered by a wall plate
700 that is secured to device 10 by way of fasteners 702.
Alternatively, device 10 can be covered by a panel that is fastened
to device 10 by way of fasteners 702. Fasteners 702 cause wall
plate 700 (or the panel) to be pressed against flange 752.
FIG. 8 is a cross-sectional view of the protective device shown in
FIG. 7. Device 10 includes a housing 754 that is configured to mate
with the front housing 750. A printed circuit board (PCB) 758 is
disposed within device 10. Resettable fuse 602 is coupled to PCB
758. Resettable fuse 602 is reset by applying a momentary force to
arm 603. Note that wall plate 700, or the panel, is not shown as
being installed in FIG. 8. Thus, probe 756 to free to extend into
the unoccupied region above flange 752 due to a biasing force of
spring 760. The biasing force of spring 760 also forces arm 603
against fuse 602, urging the fuse to re-close. Accordingly, once
the wall plate is removed, the fuse miswire circuit 600 is
re-established.
FIG. 9 shows device 10 after re-installation. Wall plate 700 (or
the panel) is pressed against flange 752 by way of fasteners 702
directing probe 756 in a downward direction. Probe 756 compresses
spring 760 so that force is no longer being applied by arm 603. As
such, fuse 602 stays in the closed position until such time as
device 10 has been properly wired. As a side benefit, if device 10
is installed, but the wall plate 700 has not been installed, fuse
602 is permanently closed. Thus circuit 600 prevents device 10 from
resetting whether device 10 is properly wired or miswired. The
rationale behind this safety feature is that without the wall
plate, the load terminals are physically accessible to the user.
Accordingly, the safety feature prevents the user from being
exposed to any voltage present on the load terminals.
It will be apparent to those of ordinary skill in the pertinent art
that modifications and variations can be made to resettable fuse
602 of the present invention depending on the form factor of PCB
758 and the disposition of arm 603. By way of example, resettable
fuse 602 may be implemented using Model X 2296 manufactured by
Thermo-Disc. Of course, those of ordinary skill in the art will
recognize that any suitable resettable fuse device may be employed
in the present invention.
FIGS. 10-11 are cross-sectional views of the protective device in
accordance with an alternate embodiment of the present invention.
Probe 800 is similar to probe 756 except that it includes striker
802. Striker 802 is configured to deflect cantilever beam 804 when
wall plate 700 is installed. Once cantilever 804 is deflected by a
predetermined amount, it clears striker 802 and rebounds to
momentarily apply a force to arm 603 to re-close the fuse.
Accordingly, miswire circuit 600 may be reactivated only by
installation of the wall plate. In an alternate embodiment, a
striker is configured so that the momentary force to arm 603 occurs
when wall plate 700 is removed. For this embodiment, reactivation
of the miswire circuit 600 does not require the installation of a
wall plate, only the removal of a wall plate.
It will be apparent to those skilled in the art that various
modifications and variations can be made to the present invention
without departing from the spirit and scope of the invention. Thus,
it is intended that the present invention cover the modifications
and variations of this invention provided they come within the
scope of the appended claims and their equivalents.
* * * * *